U.S. Patent Application Publication No. 2013/0214235 discloses a resistive random access memory device that includes a lower electrode, a changeable resistance diode formed on the lower electrode, and an upper electrode formed on the changeable resistance diode. The changeable resistance diode defines a p-n junction, has rectifying characteristics and resistive characteristics, and includes a p-type changeable resistance semiconductor layer formed on the lower electrode, and an n-type changeable resistance semiconductor layer formed on the p-type changeable resistance semiconductor layer. The p-type changeable resistance semiconductor layer is made from a material, such as SnOx (where 1.2≦x<2). The n-type changeable resistance semiconductor layer is made from a material, such as TiOx (where 1.2≦x≦1.89), and cooperates with the p-type changeable resistance semiconductor layer to define the p-n junction so as to provide the rectifying characteristics.